Recommended grip for a small knife vs a standard knife

Question

I have been studying a few movie scenes with kali style knife fighting, where the combatants appear to use a forward grip when wanting to get more range and a reverse grip for power.

I am curious if having a smaller blade (eg. push dagger or improvised weapon like small scissors) against a standard sized knife would change which grip to use to defend yourself against the larger weapon? Would you try to maximise range by using a forward grip, focus on power with a reverse grip, or simply hold it between your fingers like a push dagger and punch with it?

Answer 1

I will answer from a military/self-defense perspective. Kali is a very limited bubble within (or maybe even outside of) realistic knife fighting. It is used in media a lot because it looks good, not because it is realistic. Given, practitioners generally are superior in knife fighting because...well, it's what they do, right? But this does not mean that their methods are superior or flawless, literally just that they trained more knife fighting and can resort to trained patterns and situational awareness.

Answer

Generally, knives are held in a forward grip. That is the natural thing to do: Put the pointy end where it is supposed to be. There are some very good reasons to retain that regardless of the blade size (except maybe you are an actual expert in knife fighting and have done this a gazillion times with live blades and judged that the advantages outweigh the risks):

1. Range. As you already mentioned, you simply have a smaller range, ie. the time you have to remain within the opponent's range to land some hit is much shorter and with similar timing and speed, you will be injured more often with a reverse grip.
2. Slashing. The natural thing to do with reverse grip is a slash. Slashes do not do any damage at all as soon as the skin is covered with even the lightest kinds of cloth. You don't believe me? Put a shirt on a body doll and use a razor-sharp live blade, see how often and reliably it cuts through and how much force it takes - skin is even more elastic than the dolls, evasive movements not even considered. You'll be surprised. Thus, if you do not specifically aim for exposed body parts (naked arms, hands), slashing is meh. You can slash with a forward grip as well, obviously: instead of up and down on one side, you can only effectively slash down from left and right (given blade is directed down/away from you). Since slashing is more about psychology (keeping distance, provoking reactions, distracting) than actual damage, not a very important difference, though. One of the "weapons" of reverse grip disenchanted.
3. Force when stabbing. The main argument for that reverse grip is the supposed power. But think about it: What is more powerful? Stabbing in a frontwards movement with all your body, momentum, and weight behind it or doing it with rotational acceleration (hinge is your shoulder, which is not very strong in that position and direction) against your original momentum? Since the slashing to the body is pretty useless in most cases, another clear pro-forward-grip argument.
4. Force when ripping. Here, it becomes more interesting. One of the main points pro reverse grip is that the stab-rip-out movement is more fluent and powerful. Since this is what does make the actual, decisive damage in knife fights, this could be a good argument pro reverse grip. The thing is: If you simply turn the knife so that the blade is on the upper side in frontward grip, you gain the same advantages for abdominal hits (which are the most probable). In other words: You lose only the ripping strength when stabbing behind the collarbone while retaining all the advantages laid out above. Stabbing (and ripping) in the rib-cage region is generally a no-no since it is more probable that you will get your knife stuck in or in between rip bones and/or snapped rather than doing actual (physiological/functional) damage.
5. Forget parrying. As I said, I am talking about a case where you are not an absolute expert in knife fights. These Kali fights suggest that you can parry blades and trap arms with a reverse grip like it's nothing. While that is possible, it is much more likely that you get your finger cut (off) and/or yourself stabbed before you manage that even once. Obviously, blade size covers more of your forearm and makes it easier to parry without risking your fingers as well as to trap the opponent's arm. Thus, if the weapon gets too small (or the grip too messy, for example with scissors) to be feasible for this application, I expect every sensible person to only use a forward grip.
6. If you even have the chance, run. Knives are dangerous. Most of the time, on the streets, you get stabbed before or without you noticing anything. That is the sad reality of knife "fights". If you see a knife, run. A fight with knives in the game is one of the worst situations you can possibly get yourself in.

TL;DR

Forward grip, maybe with the blade up instead of down if you go directly for a stab-rip movement to end the fight ASAP. But definitely not and never reverse grip except you really know what you are doing and have years of practice, including live blades. Even in this case, I would say this is more due to you being more used to and better trained in a reverse grip rather than it actually being objectively better. That does not change with the relative or absolute sizes of the knives. If possible, one should avoid getting into knife fights in the first place.